The central theme of this project is a study of lipid-protein interactions in biological membranes with the eventual aim of understanding the molecular details of lipid-protein associations. The strategy is to introduce spin label analogues of specific, naturally occurring membrane phospholipids into preparations containing a single kind of functional protein, and to study lipid mobility and distribution by electron spin resonance. Lipid specificity, involving one or more sites in a background of non-selective sites on the hydrophobic surface of transmembranous proteins, has been demonstrated for the Na,K-ATPase using both single-tail and phospholipid spin labels. Our current objectives include characterization of specific lipid binding using ESR data, DSC data, electron microscopy and activity assays. We are planning to initiate work on the potential specificity of lipid-protein interactions in the association of phospholipase A2 with lipid interfaces.